NE40E version:V3R3C03B608; Network overview as below:
detailed records of fault phenomena:
KGPCE01-GI is the NE40E router which is connect to KPGGG02 GGSN and it's uplink is conncted to J Firewall. When the 3G Subscriber loss the internet connection,we fond the packet loss at Firewall.

Alarm Information

none

Handling Process

1. when the 3G internet service interruption, the GGSN will not see any alram.but PS engineer test Ping and Tracert route as Subscriber by Laptop is abnormal. the reaulst as below:
C:\Documents and Settings\Administrator>tracert 8.8.8.8 ---yahoo address
Tracing route to google-public-dns-a.google.com [8.8.8.8]
over a maximum of 30 hops:

1 * * * Request timed out.
2 188 ms 430 ms 169 ms 10.223.4.2223 2878 ms 2840 ms 2889 ms 10.223.0.101
4 * * * Request timed out.
5 * * * Request timed out.From Here we can see that it is a routing issue for GGSN,so GGSN is running normally.
2. We login NE40E, we found the traffic of interface which is connnected to Firewall is small as well as we can the tracert route in 10.223.0.101 is around 3 second delay, but we check in NE40E, did not find abnormal operation in that day as well as the log did not show any abnormity phenomena refer to attached.R&D confirm in NE40E part is normall, we chase Customer to ask J engineer to check their Firewall immediately.
3. J engineer found NAT process abnormity phenomena and the CPU utilization is higher than as usal.and reset the NAT Process, then the service recovery.